Regarding the primary battery which is not charged and produces no gas or little gas in discharge, there is known a construction such that the current generation element and plate group are packaged liquid- and gas-tight in a synthetic resin film housing. In this construction, the housing structure for the battery is very much simplified.
However, in the storage battery which is charged and produces gases in charge, mere enclosure of the plate group by such a housing does not allow withdrawal of evolved gases from the cell and with a gradual build-up of the internal pressure of the cell, the housing is ruptured to cause scattering of the electrolyte, etc. Thus, this type of housing as such is not desirabIe and a safety mechanism that permits withdrawal of gases was required.
As electrical appliances using a storage battery as a power source and, particularly, portable electrical appliances are progressively miniaturized and reduced in thickness, there has been a demand for a hermetically sealed storage battery which is similarly compact and thin and long serviceable.